# Physical and Chemical Properties of Mercury

Physical properties:

• It is shiny liquid.
• It is poisonous substance.
• It solidifies at -39 oC.
• It melts at 357.25oC.
• It is good conductor of heat and electricity.

Chemical properties:

Mercury does not react with air at normal condition but when it is heated at 350 oC, we get mercuric oxide. When it is heated below, it decomposes to give mercury and oxygen.

1. Action with air: Silver gets oxidized to to form mercuric oxide.

$$\ce{2Hg + O2->[{300^{\circ}C}]2HgO}$$
$$\ce{2HgO ->[{>300^{\circ}C}]2Hg + O2}$$

2. Action with water and alkali: Mercury being less electropositive metal and less reactive metals, it does not react with water as well as alkali.

3. Action with acid:

• Action with sulphuric acid: Since mercury is less reactive metal, it does not react with dilute acid but when mercury is heated with concentrated sulphuric acid, it forms mercuric sulphate, SO2 and water.
$$\ce{Hg + 2H2SO4->HgSO4 + 2H2O + SO2}$$
• Action with moderate nitric acid: Mercury reacts with moderate HNO3 to give mercuric nitrate, nitric oxide and water.
$$\ce{6Hg + 8HNO3->3Hg2(NO3)2 + 2NO + 4H2O}$$
• Action with conc. Nitric acid: Mercury when reacted with concentrated HNO3 gives nitrogen dioxide and mercuric nitrate.
$$\ce{6Hg + 4HNO3->Hg(NO3)2 + 2NO2 + 2H2O}$$

4. Action with aqua-regia: Aqua-regia is a mixture of 1 part nitric acid and three parts HCl. Mercury dissolves in aquaregia to give mercuric chloride.
$$\ce{3HCl + HNO3->\underset{\text{Nitrosyl chloride}}{\ce{NOCl}} + 2H2O + 2[Cl]}$$
$$\ce{Hg + 2[Cl]->HgCl2}$$

5. Action with metals: Mercury when heated with metal forms amalgum:
$$\ce{Na + Hg->[\Delta]NaHg}$$
$$\ce{Zn + Hg->[\Delta]ZnHg}$$

Note: The respective amalgum are called metal amalgum like sodium amalgum, mercuric amalgum etc.

6. Action with halogens: Mercury reacts with halogen to form respective halides.

Uses of Mercury:

•  It is used as barometric as well as thermometric liquid.
•  It is used to make calomel electrode.
• It is used for silvering mirrors.
•  It is used in mercury vapour lamps to produce UV lamps.

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